Re: [alto] ALTO Extension: A document defining multi-metrics filtering?

["RANDRIAMASY, SABINE (SABINE)" <[e-mail]>]

A few questions and comments inline to make sure I understood. If we are to document proposed filtering services, should we put separate sections, one on filtering services for the basic protocol and the other one, more prospective for protocol extensions on topologies?
Thanks
Sabine


De : [e-mail] [mailto:[e-mail]] De la part de Y. Richard Yang
Envoyé : lundi 14 octobre 2013 04:42
À : IETF ALTO
Cc : RANDRIAMASY, SABINE (SABINE); ROOME, Wendy D (Wendy); [e-mail]; Qin Wu; Young Lee; Greg Bernstein; [e-mail]; dhruv.dhody
Objet : Re: ALTO Extension: A document defining multi-metrics filtering?

Let me add on: although a filtering service can be a very useful service, it can also be quite involved, and hence the WG may need to think through the issues when designing this service. For example, there are two types of use cases:

- end-to-end: given src set {s1, s2, s3, ..., sn} and dst set {d1, d2, d3, ..., dm}, return all pairs (si, dj), where si in {s1, ..., sn} and dj in {d1, ..., dm} such that (si, dj) satisfies the constraints;
[     ] This use case corresponds to the base protocol. The requested service is the ALTO Cost Map Filtering Service w.r.t metric values. It seems easy to extend this service by extending the set of constraints with additional constraints metrics and additional logical operators.

- relay: given src s, dst d, and a relay candidate set {r1, r2, ..., rk}, return all of the ri such that s -> ri -> d satisfies the constraints.
[     ] This use case relates to a proposed ALTO extension on topologies providing cost maps where there may be several paths between an (S,D) pair. Is the ALTO Service here the ALTO Cost Map Filtering Service w.r.t metric values adapted to a multi-path topology?  The cost map here would need to include some index on the cost value w.r.t. the relay ID and the service would only return cost values on the indexed (S,D, idx) triples satisfying the constraints. If this is correct, then such a use case would well fit into filtering services for topology based ALTO  extensions.

Note that with relay, we will then need to worry about the "composition" semantics of metrics. For example, delay might be additive, loss rate (unless small and independent) may not be.
[     ] I think the composition and optimization operators should be documented in any case (I think in the "use and application" field of the RFC6390 template). Indeed, the OPTIMUM-COMPOSITION attributes may be MIN-SUM, MAX-MIN, MIN-PROD etc...

In the base protocol an e2e cost value provided by the server is already composed and abstracted. But if we have a protocol extension that details paths per sections,  then indeed e2e path cost composition may have to be done at  the ALTO Client side.

The relay could be even fancier (e.g., one-hop server detour such as Akamai one-hop detour and hence may involved two relay servers), but it may or may not be a good idea to go too complex, depending on if the WG can define a clean API (e.g., SQL select/where grammar comes to mind quickly).

Thanks!

Richard
On Sun, Oct 13, 2013 at 7:57 PM, Y. Richard Yang <[e-mail]<mailto:[e-mail]>> wrote:
Dear all,

The base ALTO protocol (http://www.ietf.org/id/draft-ietf-alto-protocol-20.txt) is mostly a single-cost-metric centric:

- The Cost Map filtering service uses only one cost-type (Sec. 11.3.2.3):

     object {
     CostType   cost-type;
     [JSONString constraints<0..*>;]
     [PIDFilter  pids;]
   } ReqFilteredCostMap;

   object {
     PIDName srcs<0..*>;
     PIDName dsts<0..*>;
   } PIDFilter;

...
 constraints  Defines a list of additional constraints on which
      elements of the Cost Map are returned.  This parameter MUST NOT be
      specified if this resource's capabilities (Section 11.3.2.4)
      indicate that constraint support is not available.  A constraint
      contains two entities separated by whitespace: (1) an operator,
      'gt' for greater than, 'lt' for less than, 'ge' for greater than
      or equal to, 'le' for less than or equal to, or 'eq' for equal to;
      (2) a target cost value.

- The Endpoint Cost service allows filtering (Sec. 11.5.1.3) as well, and is similar to Cost Map Filtering:

   object {
     CostType          cost-type;
     [JSONString       constraints<0..*>;]
     EndpointFilter    endpoints;
   } ReqEndpointCostMap;

   object {
     [TypedEndpointAddr srcs<0..*>;]
     [TypedEndpointAddr dsts<0..*>;]
   } EndpointFilter;

   constraints  Defined equivalently to the "constraints" input
      parameter of a Filtered Cost Map (see Section 11.3.2).

In other words, in the base protocol, the filtering condition and the output are based on the same Cost Metric. It is natural that the filtering and the output are based on different Cost metrics. For example, a Client asks for routingcost for only pairs whose latency is below a threshold (see use cases in http://tools.ietf.org/html/draft-randriamasy-alto-multi-cost-07).

One may argue that the filter-metric-no-equal-to-output-metric function can be implemented on top of the filter-and-output-using-one-metric function:

In particular, suppose the filtering is based on metrics M1 and M2, and the output is M3, for a set src to a set dsts. The Client can use the following three queries:

- Q1: Use single metric <M1, filter on M1, srcs, dsts> and obtains <srcs1, dsts1> in return;
- Q2: Use single metric <M2, filter on M2, srcs1, dsts1> and obtains <srcs2, dsts2> in return;
- Q3: Use single metric <M3, no filter, srcs2, dsts2> to get the final result.

Although this is not too bad, it is inconvenient. Note that preceding is first discussed by Sabine, Wendy, Nico in:
http://tools.ietf.org/html/draft-randriamasy-alto-multi-cost-07

I saw that this is also the issue discussed in
- http://tools.ietf.org/html/draft-wu-alto-json-te-01
- http://tools.ietf.org/html/draft-lee-alto-app-net-info-exchange-02

Hence, I propose that the WG extends the base protocol with this capability, as I see that it is quite useful. One issue is that I see three designs, and I am wondering if the authors are preparing on discussing their designs at the coming IETF, and if there is a possibility for a single, unified document, focusing on this issue.

Thanks a lot!

Richard